1. Field of the Invention
This invention relates to a novel adsorbent for phosphorus, a method for the dephosphorization of a phosphorus-containing liquid, and a method for the production of the adsorbent for phosphorus. More particularly, this invention relates to an adsorbent for phosphorus which essentially consists of a fired shaped product of volcanic ash possessing outstanding characteristics such as preferential adsorption of phosphorus, a large capacity for adsorption of phosphorus, excellent selectivity with respect to phosphorus, high durability and inexpensiveness, a method for dephosphorization by the use of the adsorbent mentioned above, and a method for the production of the adsorbent. The adsorbent is advantageously used for the removal of phosphorus from sewage, for example.
2. Prior Art Statement
In recent years, environmental pollution due to the eutrophication of rivers and lakes has become a serious problem. As countermeasures, use of phosphorus-free detergents in the home and treatment of sewage for dephosphorization have been promoted.
The removal of phosphorus from sewage has heretofore been performed mainly by secondary treatment attendant on the treatment of activated sludge using a microorganism. The known methods available for the secondary treatment include the lime process, the method using a metal salt such as an aluminum salt, and the method using an ion-exchange resin, for example (Kagaku Kogyosha: "Extra Issue of Kagaku Kogyo", Vol. 18 No. 1, pp 210-219, published on Jan. 1, 1974).
In the treatment by any of these methods, the ratio of phosphorus removed to the total phosphorus contained in the sewage falls short of 30%. Sewage still retaining the greater part of its original phosphorus content is released into rivers. These processes pose a number of problems. The lime process, for example, is a method which effects the removal of phosphorus by adding to the phosphorus-containing sewage under treatment an amount of lime large enough to adjust the pH value of the resultant mixture to about 10 thereby inducing occurrence of floc containing phosphorus and removing the floc from the sewage. This process entails the disadvantage that the neutralization of the sewage remaining after the removal of phosphorus necessitates consumption of a large amount of carbon dioxide, the treatment requires much time and labor, and the equipment for the treatment is expensive. The method relying on the use of a metal salt such as an aluminum salt entails the disadvantage that the gelled product obtained by the reaction with phosphorus requires a very difficult treatment. The method using an ion-exchange resin has very small selectivity with respect to phosphorus and normally suffers degradation in phosphorus removal capacity and efficiency in the presence of other coexisting cations or anions. Thus, the conventional techniques for the removal of phosphorus have a number of problems. A solution of these problems is urgently needed.